In the environment of automated controlled processes it is known to use meters for counting quantities or events and for determining frequencies. For example, FIG. 1 shows a control system known from prior art, in which meter modules in the form of software or hardware function modules are integrated in a processor system of a control device intended for process control, such as a programmable logic controller (PLC), or are directly connected to this processor system. The processor system executes software in the form of firmware and application software, which includes at least one control program. Via an internal bus in the form of a process data bus and a bus interface unit of the control device, the processor system is connected to an external bus, such as a field bus in the form of a remote bus or local bus, to which further bus subscriber units are connected, for example input or output modules. A drawback of this solution is that input data with information for a meter module originating from a bus subscriber unit and, in the reverse direction, result data from a meter module with information for a bus subscriber unit are always routed via the processor system, and that the meter modules are dependent on the processor system. On the one hand, this puts a load on the processor system, since the executed software and in particular the application software includes corresponding program steps for querying, processing and forwarding the input data and result data, which program steps must always be executed by the processor system. On the other hand, the processor system that is always involved and the software that has to be executed by the latter may have an adverse effect on latency and jitter performance of the metering function, so that fast and accurate metering of quantities or events or determining of frequencies is not possible in reliable manner, especially in the case where data are provided at high data rates and/or data volumes.
Furthermore, a high speed meter device is known from DE 42 10 015 C2, wherein a meter module implemented in hardware is disposed remote from a programmable control device and is connected thereto via a serial remote I/O line. Via a separate line, the meter module is able to receive a signal from a rotary encoder or a sensor. The meter module is operated under the control of a microprocessor. However, a drawback here is that the meter module has to be arranged remote from the control device and in the vicinity of the respective rotary encoder or sensor, from which it then receives its input signal via a separate line. Especially in large industrial installations which require a plurality of meter modules, this causes a spatial distribution of the meter modules and requires many separate connection lines and therefore results in increased installation and maintenance complexity.